The present invention relates to spiral-wound membrane cartridges, to a filter element which may be used in such cartridges, and to a method of manufacturing such cartridges without any adhesive being present in the finished cartridge. More particularly, the invention relates to a spiral membrane cartridge comprising a cylindrical permeate transport tube having a plurality of axial ports, and one or more filter elements spirally wound on the transport tube, each filter element comprising a membrane element and a feed spacer. Each membrane element comprises a permeate carrier layer interposed between a pair of membranes, e.g. semipermeable membranes, which have a heat sealable backing layer, and which are heat sealed around their periphery.
Filtration devices which contain semi-permeable membranes are used to effect liquid separations in a wide variety of applications, such as water purification, concentration of dilute mixtures or solutions, and waste treatment and/or recovery of recyclable components.
Spiral-wound membrane cartridges allow efficient filtration in such applications, by advantageously providing a large membrane surface area within a relatively small spatial volume. Spiral-wound filter cartridges are described, for example, in U.S. Pat. No. 4,902,417, the disclosure of which is incorporated herein by reference. Conventional spiral membrane cartridges are manufactured by running a bead of adhesive along the edge of a pair of flat membranes having a permeate carrier layer disposed therebetween to form a membrane element, wrapping a plurality of these membrane elements, with feed spacers interposed between the elements, in a spiral configuration, and heating the cartridge to cure the adhesive and thus seal the edges of the membrane elements. The outside of the cartridge is then typically wrapped with an adhesive tape, or otherwise secured to keep the elements from unwinding, i.e. maintain the cartridge in a spiral configuration.
One disadvantage to such conventional spiral membrane cartridges is that the use of adhesives in their manufacture reduces their usefulness in applications which involve the filtration of solvents and/or other harsh solutions. Such solvent and solutions cause degradation of the adhesives in the membrane cartridge, resulting in contamination of the retentate and/or permeate, which is particularly deleterious in pharmaceutical and biomedical applications. Breakdown of the adhesive may further result in eventual failure of the cartridge.
Additionally, the process used in the manufacture of such cartridges involves assembling the entire cartridge at once and then testing it for integrity. This necessarily means that if a single element of the device is faulty, or if there is a problem with fabrication of the cartridge, the entire device will fail the final testing. Since the cartridge cannot be disassembled after the adhesive is cured, defective cartridges must be discarded. Manufacturing is thus far less economical than it would be if each element could be tested individually prior to assembly, and defective elements discarded rather than entire assemblies. Furthermore, it would be advantageous if finished cartridges could readily be disassembled to effect repairs.
Thus it has been desired in the filtration art to provide a spiral membrane cartridge which would be highly chemically resistant, thus having good reliability over long periods of time in severe applications. It has further been desired to provide such a cartridge which is simple and economical to manufacture, and can be assembled and disassembled element-by-element.